/Engine/Plugins/Runtime/XRBase/Source/XRBase/Public/XRRenderTargetManager.h
Calculates dimensions of the render target texture for direct rendering of distortion. This implementation calculates the size based on the current value of vr.pixeldensity.
virtual void CalculateRenderTargetSize ( const class [FViewport](API\Runtime\Engine\FViewport) & Viewport, uint32 & InOutSizeX, uint32 & InOutSizeY )